The invention relates to a preliminary material for the production of composite material parts by means of hot-forming or hot isostatic pressing, which preliminary material consists of a tubular outer part which, when so desired, will form a component of the composite part after forming and of at least one core or inner part, consisting of solid and/or powdered material and comprising the other component(s) in the finished product, and of two sealing parts positioned on the front of the tubular outer part, which sealing parts may display a gas feed; and to a process for the production of the preliminary material.
Composite materials are employed to advantage in machine parts and tools which are simultaneously subjected to various demands, e.g. chemical resistance and hardness, or strength, or toughness and resistance to wear. Composite materials can be created by means of fusion-welded plating and the like, or by means of a metallic connection created by hot-forming between two or more parts.
In the creation of a metallic connection by means of hot forming, individual parts are generally enclosed in a casing (compare Swiss Patent No. 227 631), which is welded so as to be gastight (compare U.S. Pat. No. 4,640,815), and a residual cavity in the casing is filled with inert gas by means of a gas feed so as to provide an adequate metal bond or to prevent oxidation of the surface of the parts during heating to the deformation temperature, or is evacuated, whereupon the cavity is sealed (compare European Patent Document No. EP-A-0114593).
Composite materials with an inner component and with an outer component enclosing this inner component, particularly in concentric fashion, are advantageously and cost-effectively produced from preliminary material; here the outer part simultaneously serves as the casing jacket, and merely the casing base or, as the case may be, the sealing parts need be welded to the front of the outer part. A disadvantage arises when the outer part consists of a poorly weldable material or of one that can only be welded after preliminary heating, as is the case e.g. in cold-work steel (e.g. material DIN 1.2378 and the like) and when additional measures become necessary - for example, the application of so-called buffer welding with intermediate annealings of the entire outer part and with cleaning or descaling, particularly of the zone affected by the heat - before the sealing parts can be welded in gastight fashion and before the welding seam remains crack-free even during heating of the preliminary material to the treatment temperature and also free of cracks in the base material. Additional measures of this type are very expensive and do not usually possess adequate production safety. For this reason and because under certain circumstances several special materials cannot be joined by fusion welding to the sealing parts while meeting the given requirements, it is frequently necessary to produce the preliminary material by welding the parts to be joined in a lost casing of weldable material.